Overlap capacitance nanowire

ABSTRACT

A device and method for fabricating a nanowire include patterning a first set of structures on a substrate. A dummy structure is formed over portions of the substrate and the first set of structures. Exposed portions of the substrate are etched to provide an unetched raised portion. First spacers are formed about a periphery of the dummy structure and the unetched raised portion. The substrate is etched to form controlled undercut etched portions around a portion of the substrate below the dummy structure. Second spacers are formed in the controlled undercut etched portions. Source/drain regions are formed with interlayer dielectric regions formed thereon. The dummy structure is removed. The substrate is etched to release the first set of structures. Gate structures are formed including a top gate formed above the first set of structures and a bottom gate formed below the first set of structures to provide a nanowire.

RELATED APPLICATION INFORMATION

This application is a Continuation application of copending U.S. patentapplication Ser. No. 13/970,931 filed on Aug. 20, 2013, which is aContinuation application of U.S. patent application Ser. No. 13/739,182filed on Jan. 11, 2013, now U.S. Pat. No. 8,802,512 issued on Aug. 12,2014, incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to nanowires, and more particularly tonanowires having improved overlap capacitance.

2. Description of the Related Art

A nanowire is a structure having a diameter in the order of a nanometer.Nanowires promise to be the next device structure to allow devicescaling. However, nanowires are very difficult to manufacture due totheir three-dimensional nature. While several solutions have beenproposed, these solutions may include a number of drawbacks. Forexample, the proposed solutions may include a non-manufacturable processor the fabricated nanowire may have a high parasitic capacitance.

SUMMARY

A method for fabricating a nanowire includes patterning a first set ofstructures on a substrate. A dummy structure is formed over portions ofthe substrate and the first set of structures. Exposed portions of thesubstrate are etched to provide an unetched raised portion. Firstspacers are formed about a periphery of the dummy structure and theunetched raised portion. The substrate is etched to form controlledundercut etched portions around a portion of the substrate below thedummy structure. Second spacers are formed in the controlled undercutetched portions. Source/drain regions are formed with interlayerdielectic regions formed thereon. The dummy structure is removed. Thesubstrate is etched to release the first set of structures. Gatestructures are formed including a top gate formed above the first set ofstructures and a bottom gate formed below the first set of structures toprovide a nanowire.

A method for fabricating a nanowire includes patterning fin structureson a substrate. A dummy structure is formed over portions of thesubstrate and the fin structures. Exposed portions of the substrate areetched to provide an unetched raised portion. First sidewall spacers areformed about a periphery of the dummy structure and the unetched raisedportion. The substrate is etched to form controlled undercut etchedportions around a portion of the substrate below the dummy structure.Second spacers are formed in the controlled undercut etched portions.Source/drain regions are formed with interlayer dielectic regions formedthereon. The dummy structure is removed. The substrate is etched torelease the fin structures. Metal gate structures are formed including atop gate formed above the fin structures and a bottom gate formed belowthe fin structures to provide a nanowire such that edges of the top gateand the bottom gate are aligned.

A semiconductor device includes one or more structures formed on asubstrate. A top gate is formed above the one or more structures andbetween first spacers. A bottom gate is formed below the one or morestructures and between second spacers. Source/drain regions are formedhaving interlayer dielectric regions formed thereon.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1A is a top view of a semiconductor device including a substratehaving fin structures and a dummy structure formed thereon, inaccordance with the present principles;

FIG. 1B is a cross-sectional view taken at section line 1A-1A of FIG.1A, in accordance with the present principles;

FIG. 1C is a cross-sectional view taken at section line 1C-1C of FIG.1A, in accordance with the present principles;

FIG. 1D is a cross-sectional view taken at section line 1B-1B of FIG.1A, in accordance with the present principles;

FIG. 2A is a top view of the structure of FIG. 1A having an etchedsubstrate surface, in accordance with the present principles;

FIG. 2B is a cross-sectional view taken at section line 2A-2A of FIG.2A, in accordance with the present principles;

FIG. 2C is a cross-sectional view taken at section line 2C-2C of FIG.2A, in accordance with the present principles;

FIG. 2D is a cross-sectional view taken at section line 2B-2B of FIG.2A, in accordance with the present principles;

FIG. 3A is a top view of the structure of FIG. 2A having spacers formedabout a periphery of the dummy structure, in accordance with the presentprinciples;

FIG. 3B is a cross-sectional view taken at section line 3A-3A of FIG.3A, in accordance with the present principles;

FIG. 3C is a cross-sectional view taken at section line 3C-3C of FIG.3A, in accordance with the present principles;

FIG. 3D is a cross-sectional view taken at section line 3B-3B of FIG.3A, in accordance with the present principles;

FIG. 4A is a top view of the structure of FIG. 3A, wherein the substrateis further etched to provide undercut portions, in accordance with thepresent principles;

FIG. 4B is a cross-sectional view taken at section line 4A-4A of FIG.4A, in accordance with the present principles;

FIG. 4C is a cross-sectional view taken at section line 4C-4C of FIG.4A, in accordance with the present principles;

FIG. 4D is a cross-sectional view taken at section line 4B-4B of FIG.4A, in accordance with the present principles;

FIG. 5A is a top view of the structure of FIG. 4A having spacers formedalong a surface of the substrate, in accordance with the presentprinciples;

FIG. 5B is a cross-sectional view taken at section line 5A-5A of FIG.5A, in accordance with the present principles;

FIG. 5C is a cross-sectional view taken at section line 5C-5C of FIG.5A, in accordance with the present principles;

FIG. 5D is a cross-sectional view taken at section line 5B-5B of FIG.5A, in accordance with the present principles;

FIG. 6A is a top view of the structure of FIG. 5A having source/drainregions and interlayer dielectric regions formed and the dummy structureremoved, in accordance with the present principles;

FIG. 6B is a cross-sectional view taken at section line 6A-6A of FIG.6A, in accordance with the present principles;

FIG. 6C is a cross-sectional view taken at section line 6C-6C of FIG.6A, in accordance with the present principles;

FIG. 6D is a cross-sectional view taken at section line 6B-6B of FIG.6A, in accordance with the present principles;

FIG. 7A is a top view of the structure of FIG. 6A having portions of thesubstrate etched to release the fin structures, in accordance with thepresent principles;

FIG. 7B is a cross-sectional view taken at section line 7A-7A of FIG.7A, in accordance with the present principles;

FIG. 7C is a cross-sectional view taken at section line 7C-7C of FIG.7A, in accordance with the present principles;

FIG. 7D is a cross-sectional view taken at section line 7B-7B of FIG.7A, in accordance with the present principles;

FIG. 8A is a top view of the structure of FIG. 7A having metal gatesformed above and below the fin structures, in accordance with thepresent principles;

FIG. 8B is a cross-sectional view taken at section line 8A-8A of FIG.8A, in accordance with the present principles;

FIG. 8C is a cross-sectional view taken at section line 8C-8C of FIG.8A, in accordance with the present principles;

FIG. 8D is a cross-sectional view taken at section line 8B-8B of FIG.8A, in accordance with the present principles; and

FIG. 9 is a block/flow diagram showing a system/method for fabricatingnanowires, in accordance with the present principles.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the present principles, a method and a device areprovided for fabricating a nanowire having improved overlap capacitance.A semiconductor device includes a substrate, which may include a buriedoxide layer. Fins are patterned thereon and a polysilicon dummystructure is formed over a portion of the substrate and fins. Exposedportions of the substrate are etched and first spacers are formed arounda periphery of the dummy structure and unetched raised portions of thesubstrate.

The substrate is further etched to provide a controlled undercut of thesubstrate below the first spacers and the fins. Second spacers areformed in the undercut portions of the substrate. Source/drain regionsare formed, and interlayer dielectric layers are formed thereon toprovide electoral separation. The dummy structure is then removed toetch the substrate, thereby releasing the fins. This may include etchingportions of the substrate between the second spacers. Metal gatestructures are formed to provide a top gate and a bottom gate.Advantageously, the edges of the top gate and bottom gate are aligned toprevent stray capacitance between the gates. The present principles arecompatible with standard fin field effect transistor processing and is,therefore, very manufacturable.

It is to be understood that the present invention will be described interms of a given illustrative architecture having a wafer; however,other architectures, structures, substrate materials and processfeatures and steps may be varied within the scope of the presentinvention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

A design for an integrated circuit chip of photovoltaic device may becreated in a graphical computer programming language, and stored in acomputer storage medium (such as a disk, tape, physical hard drive, orvirtual hard drive such as in a storage access network). If the designerdoes not fabricate chips or the photolithographic masks used tofabricate chips, the designer may transmit the resulting design byphysical means (e.g., by providing a copy of the storage medium storingthe design) or electronically (e.g., through the Internet) to suchentities, directly or indirectly. The stored design is then convertedinto the appropriate format (e.g., GDSII) for the fabrication ofphotolithographic masks, which typically include multiple copies of thechip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems and methods according to various embodiments of the presentinvention. It should be noted that, in some alternative implementations,the functions noted in the blocks may occur out of the order noted inthe figures. For example, two blocks shown in succession may, in fact,be executed substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. It will also be noted that each block of the block diagramsand/or flowchart illustration, and combinations of blocks in the blockdiagrams and/or flowchart illustration, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts, or combinations of special purpose hardware and computerinstructions.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1A, a top-down view of asemiconductor device 10 is illustratively depicted in accordance withone embodiment. FIG. 1B shows a cross-sectional view of thesemiconductor device 10 at section line 1A-1A. FIG. 1C shows across-sectional view of the semiconductor device 10 at section line1C-1C. FIG. 1D shows a cross-sectional view of the semiconductor device10 at section line 1B-1B.

The device 10 includes a substrate 16. The substrate 16 preferablyincludes a buried oxide (BOX) layer, however other materials may beemployed. For example, substrate 16 may include any suitable material,such as, e.g., a Semiconductor-on-Insulator (SOI) or bulk substrate thatmay include Gallium, Arsenide, monocrystalline silicon, Germanium, orany other suitable material or combination of materials.

Fins 14 are patterned over the substrate 16 using known techniques. Fins14 preferably have a width of or about, e.g., 8 nanometers. Fins 14 mayinclude any suitable material, such as, e.g., Gallium, Arsenide,monocrystalline silicon, Germanium, or any other suitable material orcombination of materials. A dummy structure 12 is formed over a portionof the substrate 16 and fins 14. The dummy structure 12 preferablyincludes polysilicon, however other suitable material or combination ofmaterials may be employed. The dummy structures 12 may be formed by anysuitable technique (e.g., deposition). In some embodiments, thesubstrate 16 further comprises other features or structures that areformed in or on the semiconductor substrate 16 in previous steps.

Referring now to FIG. 2A, the semiconductor device 10 of FIG. 1A isprocessed to form etched portions 18. FIG. 2B shows a cross-sectionalview of the semiconductor device 10 at section line 2A-2A. FIG. 2C showsa cross-sectional view of the semiconductor device 10 at section line2C-2C. FIG. 2D shows a cross-sectional view of the semiconductor device10 at section line 2B-2B.

Exposed portions 18 of the substrate 16 are etched to formed unetchedraised portions 19 of the substrate. The exposed portions 18 may includeportions of the substrate 16 that are not covered by dummy structure 12and/or fins 14. Etching preferably includes reactive ion etching (RIE),however other forms of etching are also contemplated (e.g., wet chemicaletch, dry plasma etch, combinations of wet chemical etch and dry plasmaetch, etc.). Etched substrate portions 18 are preferably etched to adepth of or about, e.g., 5 nanometers.

Referring now to FIG. 3A, the semiconductor device 10 of FIG. 2A isprocessed to form first offset spacers 20 about a periphery of the dummystructure 12 and unetched raised portions 19 of the substrate. FIG. 3Bshows a cross-sectional view of the semiconductor device 10 at sectionline 3A-3A. FIG. 3C shows a cross-sectional view of the semiconductordevice 10 at section line 3C-3C. FIG. 3D shows a cross-sectional view ofthe semiconductor device 10 at section line 3B-3B.

The first spacers 20 may include a nitride material, for example. Thespacer material may be conformally deposited over the device 10 andetched (e.g., RIE, etc.) to leave first spacers 20 along the sidewallsof the dummy structure and the unetched raised portions 19 of thesubstrate. The first spacers 20 are preferably at half thickness of thedesired offset spacer thickness, to have a width of or about, e.g., 5nanometers.

Referring now to FIG. 4A, processing of semiconductor device 10 of FIG.3A continues to form undercut portions 22 of the substrate 16. FIG. 4Bshows a cross-sectional view of the semiconductor device 10 at sectionline 4A-4A. FIG. 4C shows a cross-sectional view of the semiconductordevice 10 at section line 4C-4C. FIG. 4D shows a cross-sectional view ofthe semiconductor device 10 at section line 4B-4B.

The surface of the substrate 16 is etched by, e.g., a buffered oxideetch (BOE) using hydrofluoric (HF) acid. HF acid is preferably appliedto the surface of the substrate 16 such that undercut portions 22beneath the fins 14 are also etched. The undercut portions 22 includeportions of the substrate 16 beneath the fin 14 and first spacers 20,while portions of the substrate under the dummy structure 12 and abovelayers (e.g., fins 14, spacers 20) remain unaffected. The undercutportions 22 are controlled by adjusting the dilution of HF acid appliedin the BOE. The substrate 16 is preferably etched to a depth of orabout, e.g., 5 nanometers. It should be understood that any suitableetching technique may be employed, such as, e.g., wet chemical etchmethod, dry plasma etch method, etc.

Referring now to FIG. 5A, the semiconductor device 10 of FIG. 4 isprocessed to form second offset spacers 24 formed over the first offsetspacers 20 and in the undercut portions 22. FIG. 5B shows across-sectional view of the semiconductor device 10 at section line5A-5A. FIG. 5C shows a cross-sectional view of the semiconductor device10 at section line 5C-5C. FIG. 5D shows a cross-sectional view of thesemiconductor device 10 at section line 5B-5B.

The second spacers 24 may include, e.g., nitride material. The spacermaterial may be conformally deposited over the surface of the device 10and etched (e.g., RIE, etc.) to remove horizontal components of thespacer material, leaving second spacers 24 over first spacers 20. Thesecond spacers 24 are formed at half size of the desired thickness overfirst spacers 20, to form full size sidewall spacers. Advantageously,the second spacers 24 formed in the undercut portions 22 remain afterthe etch since they are covered by the fins 14. The second spacers 24preferably have a thickness of or about, e.g., 5 nanometers.

Referring now to FIG. 6A, the semiconductor device 10 of FIG. 5 isprocessed. FIG. 6B shows a cross-sectional view of the semiconductordevice 10 at section line 6A-6A. FIG. 6C shows a cross-sectional view ofthe semiconductor device 10 at section line 6C-6C. FIG. 6D shows across-sectional view of the semiconductor device 10 at section line6B-6B.

Source/drain (S/D) regions 26 are formed over the substrate 16 and fins14. An epitaxy is preferably employed to form the S/D regions 26, whichmay include epitaxially growing silicon, germanium, or other suitablematerial or combination of materials. Interlayer dielectric (ILD)regions 28 are formed over S/D regions 26 to provide electricalseparation. ILD regions 28 may be formed by depositing dielectricmaterial over the surface of the device 10 and planarizing to thesurface of the dummy structure 12. The dummy structure 12 is thenremoved by applying, e.g., any suitable etching technique to selectivelyetch the polysilicon of the dummy structure 12.

Referring now to FIG. 7A, the semiconductor device 10 of FIG. 6A isprocessed to etch a portion 30 of the substrate 16 to release fins 14.FIG. 7B shows a cross-sectional view of the semiconductor device 10 atsection line 7A-7A. FIG. 7C shows a cross-sectional view of thesemiconductor device 10 at section line 7C-7C. FIG. 7D shows across-sectional view of the semiconductor device 10 at section line7B-7B.

Exposed portions of the substrate 16 are etched to release fins 14.Etching may include employing a BOE with HF acid. HF acid may be appliedto the exposed surface of the substrate 16 such that an undercut portion30 is etched. Undercut portion 30 may be controlled by adjusting thedilution of the HF acid. The undercut portion 30 may include the portionbelow the fins 14 and between the second spacers 24. Other suitableetching techniques may also be employed. Substrate 16 is preferablyetched to a depth of or about, e.g., 6 nanometers.

Referring now to FIG. 8A, the semiconductor device 10 of FIG. 7A isprocessed to form gate structures 32. FIG. 8B shows a cross-sectionalview of the semiconductor device 10 at section line 8A-8A. FIG. 8C showsa cross-sectional view of the semiconductor device 10 at section line8C-8C. FIG. 8D shows a cross-sectional view of the semiconductor device10 at section line 8B-8B.

Gate structures 32 preferably include metal gate structures. Metal gatematerial may be deposited over the device 10 and planarized, e.g.,chemical-mechanical planarization (CMP), down to the surface of the ILDregions 28. Other suitable techniques may also be employed. Gatestructures 32 include a top gate 34 and a bottom gate 36. The edges ofthe top gate 34 and the bottom gate 36 are preferably aligned such thatthere is no overlap to cause stray capacitance between the gates.Advantageously, the second spacers 24 (e.g., a nitride layer) are onboth sides of the bottom gate 36 to prevent expansion of the bottom gate36 and maintain the alignment of the edges of the top gate 34 and bottomgate 36. Fins 14 are provided as nanowires. As can be seen, the gatestructures 32 are formed on all four sides of each of the fins 14.

Referring now to FIG. 9, a block/flow diagram showing a method 100 forfabricating a nanowire is illustratively depicted in accordance with oneillustrative embodiment. In block 102, a first set of structures arepatterned on a substrate. The substrate preferably includes a BOX layer,however other suitable materials may be employed, such as, e.g., an SOIor bulk substrate material or combination of materials. The substratemay include other features formed in or on the substrate in previousprocess steps. In one embodiment, the first set of structures includesat least one fin, which may be patterned using any suitable lithographicmethod. The at least one fin may include any suitable material.

In block 104, a dummy structure is formed over a portion of thesubstrate and the first set of structures. The dummy structurepreferably includes polysilicon, however other suitable material orcombination of materials may also be employed. The dummy structure maybe formed by, e.g., deposition or any other suitable method.

In block 106, exposed portions of the substrate are etched to form anunetched raised portion of the substrate. Exposed portions may includeportions of the substrate that are not covered by the dummy structure orthe first set of structures. Etching may include RIE, or other suitableetching methods.

In block 108, first spacers are formed about a periphery of the dummystructure and the unetched raised portion of the substrate. The firstspacers include sidewall spacers and may be formed from a siliconnitride (nitride) or other similar material. The first spacers arepreferably formed at half of a desired width.

In block 110, the substrate is etched to form undercut etched portionsaround a portion of the substrate below the dummy structure. Undercutetched portions of the substrate may include portions below the firstspacers and below the first set of structures. Preferably, portions ofthe substrate not covered by the dummy structure are etched, while abovelayers remain unaffected. Undercut etched portions of the substrate arecontrolled by adjusting etching parameters (e.g., dilution of HF acid,etc.) Etching may include a BOE using HF acid, however other suitableetching methods may also be applied. In block 112, second spacers areformed over the first spacers and in the undercut portions. The secondspacers may be formed from a silicon nitride (nitride) or other similarmaterial. The second spacers are preferably at half of the desiredwidth, such that the second spacers formed over the first spacers formfull sidewall spacers.

In block 114, source/drain regions and interlayer dielectric regions areformed. Forming S/D regions may include epitaxially growing silicon,germanium, or other suitable material or combination of materials. ILDregions are formed over S/D regions by, e.g., deposition andplanarization to electrically separate devices. In block 116, the dummystructure is selectively removed by applying any suitable etching method(e.g., reactive ion etch, etc.).

In block 118, portions of the substrate are etched to release the firstset of structures. The etched portions preferably include portionsbetween the second spacers and below the first set of structures.Etching may include any suitable etching method.

In block 120, gate structures are formed. Preferably, metal gatestructures are formed by deposition and chemical-mechanicalplanarization, or by any other suitable methods. Metal gates may beformed above and below the first set of structures to form a top gateand a bottom gate. The edges of the top gate and bottom gate arepreferably aligned such that there is no overlap to cause straycapacitance between the gates. Second spacers (e.g., a nitride layer)are on both sides of the bottom gate to prevent the expansion of thebottom gate and maintain the alignment between the edges of the top gateand the bottom gate. The first set of structures are provided asnanowires. The gate structures are formed on all four sides of each ofthe structures.

In block 122, additional processing may be performed. Additionalprocessing may include forming field effect transistors, forming otherstructures, etc.

Having described preferred embodiments of a system and method forimproved overlap capacitance nanowire (which are intended to beillustrative and not limiting), it is noted that modifications andvariations can be made by persons skilled in the art in light of theabove teachings. It is therefore to be understood that changes may bemade in the particular embodiments disclosed which are within the scopeof the invention as outlined by the appended claims. Having thusdescribed aspects of the invention, with the details and particularityrequired by the patent laws, what is claimed and desired protected byLetters Patent is set forth in the appended claims.

What is claimed is:
 1. A semiconductor device comprising: a top gate present on an upper surface of at least one fin structure having a first spacer present on a first sidewall of the top gate; and a bottom gate present on a lower surface of the fin structure having a second sidewall that is aligned with the first sidewall of the top gate, wherein a second spacer is present on the second sidewall having a vertical portion aligned with a vertical portion of the first spacer, and a horizontal portion of the second spacer extending along a portion of the lower surface of the fin structure beyond the width of the first spacer.
 2. The semiconductor device of claim 1 further comprising a substrate that is supporting the at least one fin structure.
 3. The semiconductor device of claim 1, wherein the vertical portion of the second spacer is formed on a portion of the first spacer.
 4. The semiconductor device of claim 2, wherein the horizontal portion of the second spacer is present between the substrate and portions of the at least one fin structure, wherein the horizontal portion of the second spacer extends along an entire length of the at least one fin structure that extends beyond a sidewall of the top gate.
 5. The semiconductor device of claim 1 further comprising source and drain regions on portions of the at least one fin structure adjacent to the upper gate and the lower gate.
 6. The semiconductor device as recited in claim 2, wherein the bottom gate is formed above the substrate.
 7. The semiconductor device as recited in claim 1, wherein the bottom gate is laterally disposed between undercut etched portions.
 8. The semiconductor device as recited in claim 7, wherein the undercut etched portions include dielectric material.
 9. The semiconductor device as recited in claim 1, wherein the top gate includes a top metal gate and the bottom gate includes a bottom metal gate.
 10. The semiconductor device as recited in claim 1, wherein the at least one fin includes one or more fins for a nanowire. 